# set(可迭代对象)    无序，不重复
a = set("ABCDE")
print(a)
print(a.add('D'))
print(type({'J','K','Q'}))
b = set(["好","一般","差"])
print(b)

# a = frozenset('abcde')
b.update(["很好","差"])
print(b)
print(a.difference("aBCDE"))
print(a)
print(a.difference_update("aBCDE"))
print(a)